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What Is a Drug Allergy?
A drug allergy is an allergic reaction to a medication. Find out how to know if you have one and what to do about it.

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A drug allergy is an allergic reaction to a drug or medication. An allergic reaction means that your immune system identifies the drug as foreign and acts to eliminate it from your body. Your immune system responds to foreign substances in multiple ways, all of which lead to increased inflammation. These inflammatory responses may cause you to have symptoms such as rash, fever, or breathing difficulties.

True drug allergy is not common. According to the World Allergy Organization (WAO), it occurs in 3 to 5 percent of hospitalized patients. Additionally, less than 10 percent of adverse drug reactions are caused by genuine drug allergy.

Is A Drug Allergy Dangerous?

The symptoms of drug allergy may be so mild that you hardly notice them. You might experience nothing more than a slight rash. A severe drug allergy, however, can be life threatening. Anaphylaxis is a sudden, severe, whole-body reaction to a drug or other allergen. It occurs soon after exposure to the substance and includes symptoms such as irregular heartbeat, difficulty breathing, swelling, and unconsciousness. If not treated immediately, anaphylaxis can be fatal.

How Does Drug Allergy Work?

Your immune system is designed to protect you from foreign invaders, such as viruses, bacteria, parasites, and other toxic substances. When a drug enters your body, your immune system may mistake it for one of these invaders. This might happen the first time you take the drug, or it may not be until after you’ve taken it many times with no problems.

As soon as the drug is identified as a threat, your immune system begins to make antibodies. These are special proteins programmed to attack just that one drug.

Some drugs, such as morphine, aspirin, some chemotherapy drugs, and the dyes used in some X-rays, can cause an anaphylaxis-type reaction the first time they are used. This does not involve the immune system and is not a true allergy. However, the symptoms and treatment are the same as for true anaphylaxis, and it is just as life threatening.

What Is the Difference Between Side Effects and Drug Allergy?

A side effect is any secondary action of a drug. It may be either harmful or beneficial. It is something that might occur in any healthy person taking the drug and does not necessarily involve the immune system.

For example, aspirin, which is used to treat headache pain, often causes stomach upset (an adverse side effect) and reduces your chance of heart attack and stroke (a beneficial side effect); acetaminophen (Tylenol), which is used for pain, is associated with liver damage (an adverse side effect); nitroglycerin, which is used to widen blood vessels and improve blood flow, also improves mental function (a beneficial side effect).

A drug allergy is a group of symptoms caused by allergic reaction to a drug. An allergic reaction is the result of response by your immune system.

What Is the Long-Term Outlook for Someone with Drug Allergy?

Your immune system can change over time, and it is possible that your allergy will diminish or go away. However, it could also get worse. If you have any symptoms of drug allergy or any side effects to medication you are taking, discuss them with your doctor.

Mild allergic reactions to drugs can usually be controlled with other medications to block the immune response and reduce symptoms. Such medications may include:

  • antihistamines: These are drugs that calm symptoms of an allergic reaction by blocking the production of histamine, a substance the body produces in response to what it perceives as a harmful substance. The release of histamine may trigger allergic symptoms such as swelling, itching, or irritation.
  • corticosteroids: These help to reduce the inflammation that may be causing swelling of airways and other serious symptoms. Corticosteroids may be given orally, topically, or by injection.
  • bronchodilators: If you experience wheezing or coughing, your doctor might recommend a bronchodilator. This will open the air passages and make breathing easier.

If you have had a previous allergic reaction to a drug, you should avoid using the drug in the future. Your doctor will usually be able to use another drug to treat you.

In some cases, it may be preferable to use the drug that you are known to be allergic to. If this happens, you may be given antihistamines, corticosteroids, or bronchodilators before taking the drug. This should only be done under close medical supervision.

In some cases, you can be desensitized to a drug. This involves repeated exposure to the drug. Your doctor will start with a very low dose, which will be gradually increased until you develop a tolerance. You should not try to do this on your own. The procedure requires the close supervision of an allergist.

If you know that you are allergic to any drug, be sure to inform all of your medical providers, including your dentist and any other care provider who may prescribe medication. It is a good idea to wear a bracelet or necklace or carry a card that identifies your drug allergy—in an emergency, this could save your life.

Written by: the Healthline Editorial Team
Edited by:
Medically Reviewed by: Aleah Rodriguez, PharmD
Published: Aug 27, 2014
Published By: Healthline Networks, Inc.
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